docs: def jp_compose(s, base=None):
      """ append/encode a string to json-pointer
      """
      if s == None:
          return base
  
      ss = [s] if isinstance(s, six.string_types) else s
      ss = [s.replace('~', '~0').replace('/', '~1') for s in ss]
      if base:
          ss.insert(0, base)
      return '/'.join(ss)